diff --git a/libexec/flua/modules/lposix.c b/libexec/flua/modules/lposix.c
--- a/libexec/flua/modules/lposix.c
+++ b/libexec/flua/modules/lposix.c
@@ -165,6 +165,39 @@
 
 }
 
+static int
+lua_dup2(lua_State *L)
+{
+	int error, oldd, newd;
+
+	enforce_max_args(L, 2);
+
+	oldd = luaL_checkinteger(L, 1);
+	if (oldd < 0) {
+		error = EBADF;
+		goto err;
+	}
+
+	newd = luaL_checkinteger(L, 2);
+	if (newd < 0) {
+		error = EBADF;
+		goto err;
+	}
+
+	error = dup2(oldd, newd);
+	if (error >= 0) {
+		lua_pushinteger(L, error);
+		return (1);
+	}
+
+	error = errno;
+err:
+	lua_pushnil(L);
+	lua_pushstring(L, strerror(error));
+	lua_pushinteger(L, error);
+	return (3);
+}
+
 static int
 lua_fnmatch(lua_State *L)
 {
@@ -479,6 +512,7 @@
 	REG_SIMPLE(_exit),
 	REG_SIMPLE(chown),
 	REG_DEF(close, lua_pclose),
+	REG_SIMPLE(dup2),
 	REG_SIMPLE(fork),
 	REG_SIMPLE(getpid),
 	REG_SIMPLE(pipe),